The American Community Survey (ACS) is a relatively new survey conducted by the U.S. Census Bureau. It uses a series of monthly samples to produce annually updated data for the same small areas (census tracts and block groups) formerly surveyed via the Decennial Census long-form sample. Five years of data collection will be required to produce these small-area data. Once the Census Bureau has collected 5 years of data, new small-area data will be produced annually. The Census Bureau will produce 3-year and 1-year data products for larger geographic areas. The ACS includes people living in both housing units (HUs) and group quarters (GQs). The ACS is conducted throughout the United States and in Puerto Rico, where it is called the Puerto Rico Community Survey (PRCS). For ease of discussion, the term ACS is used here to represent both surveys.

The American Community Survey releases meaningful data products on the Census Bureau' s American FactFinder website. To address other requests, the American Community Survey produces the Summary File product that contains the complete set of the detailed tables in a comma delimited file format to allow for importation of this data into databases, spreadsheets, SAS datasets, and other formats. The American Community Survey' s Summary File follows the approach taken for the Census 2000 Summary File 3 format (To see SF3 format, please visit http://www.census.gov/census2000/sumfile3.html). The American Community Survey Summary File consists of approximately 1,300 detailed tables of demographic, social, economic, and housing characteristics for the 1-year and 3-year products.

The American Community Survey detailed tables contain both a base and collapsed version. The base tables provide detailed information on a given topic, and the collapsed tables provide a consolidated version of a base table. The base table name begins with the letter 'B' and the collapsed table name begins with the letter 'C' to allow for easy identification.

The American Community Survey covers a broad spectrum of geographic areas within the United States and Puerto Rico. The American Community Survey divides characteristics into to demographic, social, housing, and economic topics.

There are both legal and statistical American Indian, Alaska Native, and native Hawaiian entities for which the U.S. Census Bureau provides data for Census 2000. The legal entities consist of federally recognized American Indian reservations and off-reservation trust land areas, the tribal subdivisions that can divide these entities, state recognized American Indian reservations, Alaska Native Regional Corporations, and Hawaiian home lands. The statistical entities are Alaska Native village statistical areas, Oklahoma tribal statistical areas, tribal designated statistical areas, and state designated American Indian statistical areas. Tribal subdivisions can exist within the statistical Oklahoma tribal statistical areas.

In all cases, these areas are mutually exclusive in that no American Indian, Alaska Native, or Hawaiian home land can overlap another tribal entity, except for tribal subdivisions, which subdivide some American Indian entities, and Alaska Native village statistical areas, which exist within Alaska Native Regional Corporations. In some cases where more than one tribe claims jurisdiction over an area, the U.S. Census Bureau creates a joint use area as a separate entity to define this area of dual claims.

Alaska Native Regional Corporations (ANRCs) are corporate entities established to conduct both business and nonprofit affairs of Alaska Natives pursuant to the Alaska Native Claims Settlement Act of 1972 (Public Law 92-203). Twelve ANRCs are geographic entities that cover most of the state of Alaska (the Annette Island Reserve-an American Indian reservation-is excluded from any ANRC). (A thirteenth ANRC represents Alaska Natives who do not live in Alaska and do not identify with any of the 12 corporations; the U.S. Census Bureau does not provide data for this ANRC because it has no geographic extent.) The boundaries of ANRCs have been legally established. The U.S. Census Bureau offers representatives of the 12 nonprofit ANRCs the opportunity to review and update the ANRC boundaries. The Census Bureau first provided data for ANRCs for the 1990 census.

Each ANRC is assigned a five-digit Federal Information Processing Standards (FIPS) code, which is assigned in alphabetical order by ANRC name.

Federal American Indian reservations are areas that have been set aside by the United States for the use of tribes, the exterior boundaries of which are more particularly defined in the final tribal treaties, agreements, executive orders, federal statutes, secretarial orders, or judicial determinations. The U.S. Census Bureau recognizes federal reservations as territory over which American Indian tribes have primary governmental authority. These entities are known as colonies, communities, pueblos, rancherias, ranches, reservations, reserves, villages, Indian communities, and Indian villages. The Bureau of Indian Affairs maintains a list of federally recognized tribal governments. The Census Bureau contacts representatives of American Indian tribal governments to identify the boundaries for federal reservations.

Some state governments have established reservations for tribes recognized by the state. A governor-appointed state liaison provides the names and boundaries for state recognized American Indian reservations to the U.S. Census Bureau. The names of these reservations are followed by "(State)" in census data presentations.

Federal reservations may cross state boundaries, and federal and state reservations may cross county, county subdivision, and place boundaries. For reservations that cross state boundaries, only the portions of the reservations in a given state are shown in the data products for that state. Lands that are administered jointly and/or are claimed by two tribes, whether federally or state recognized, are called "joint use areas," and are treated as if they are separate American Indian reservations for statistical purposes. The entire reservations are shown in data products for the United States. The U.S. Census Bureau first provided data for American Indian reservations in the 1970 census.
Each federal American Indian reservation is assigned a four-digit census code ranging from 0001 through 4999. These census codes are assigned in alphabetical order of American Indian reservation names nationwide, except that joint use areas appear at the end of the code range. Each state American Indian reservation is assigned a four-digit census code ranging from 9000 through 9499. Each American Indian reservation also is assigned a five-digit Federal Information Processing Standards (FIPS) code; because FIPS codes are assigned in alphabetical sequence within each state, the FIPS code is different in each state for reservations that include territory in more than one state.

Trust lands are areas for which the United States holds title in trust for the benefit of a tribe (tribal trust land) or for an individual Indian (individual trust land). Trust lands can be alienated or encumbered only by the owner with the approval of the Secretary of the Interior or his/her authorized representative. Trust lands may be located on or off of a reservation. The U.S. Census Bureau recognizes and tabulates data for reservations and off-reservation trust lands because American Indian tribes have primary governmental authority over these lands. Primary tribal governmental authority generally is not attached to tribal lands located off the reservation until the lands are placed in trust.

In the U.S. Census Bureau's data tabulations, off-reservation trust lands always are associated with a specific federally recognized reservation and/or tribal government. Such trust lands may be located in more than one state. Only the portions of off-reservation trust lands in a given state are shown in the data products for that state; all off-reservation trust lands associated with a reservation or tribe are shown in data products for the United States. The Census Bureau first provided trust land data for off-reservation tribal trust lands in the 1980 census; in 1990, the trust land data included both tribal and individual trust lands. The Census Bureau does not identify restricted fee land or land in fee simple status as a specific geographic category.

In decennial census data tabulations, off-reservation trust lands are assigned a four-digit census code and a five-digit Federal Information Processing Standards (FIPS) code that is the same as that for the reservation with which they are associated. As with reservations, FIPS codes for off-reservation trust lands are unique within state, so they will differ if they extend into more than one state. The FIPS codes for such off-reservation trust lands are the same as those for the associated reservation. In the TIGER/Line® products, a letter code-"T" for tribal and "I" for individual-identifies off-reservation trust lands. In decennial census data tabulations, a trust land flag uniquely identifies off-reservation trust lands. Printed reports show separate tabulations for all off-reservation trust land areas, but do not provide separate tabulations for the tribal versus individual trust lands. Trust lands associated with tribes that do not have a reservation are presented and coded by tribal name, interspersed alphabetically among the reservation names.

American Indian tribal subdivisions are administrative subdivisions of federally recognized American Indian reservations, off-reservation trust lands, or Oklahoma tribal statistical areas (OTSAs), known as areas, chapters, communities, or districts. These entities are internal units of self-government or administration that serve social, cultural, and/or economic purposes for the American Indians on the reservations, off-reservation trust lands, or OTSAs.

The U.S. Census Bureau obtains the boundary and name information for tribal subdivisions from tribal governments. The Census Bureau first provided data for American Indian tribal subdivisions in the 1980 census when it identified them as "American Indian subreservation areas." It did not provide data for these entities in conjunction with the 1990 census. Each American Indian tribal subdivision is assigned a three-digit census code that is alphabetically in order and unique within each reservation, associated off-reservation trust land, and OTSA.

Each tribal subdivision also is assigned a five-digit Federal Information Processing Standards (FIPS) code. FIPS codes are assigned alphabetically within state; the FIPS codes are different in each state for tribal subdivisions that extend into more than one state.

Hawaiian home lands (HHLs) are areas held in trust for native Hawaiians by the state of Hawaii, pursuant to the Hawaiian Homes Commission Act of 1920, as amended. The U.S. Census Bureau obtained the names and boundaries of HHLs from state officials. HHLs are a new geographic entity for Census 2000. Each HHL area is assigned a national four-digit census code ranging from 5000 through 5499 based on the alphabetical sequence of each HHL name.

Each HHL also is assigned a five-digit Federal Information Processing Standards (FIPS) code in alphabetical order within the state of Hawaii.

State designated American Indian statistical areas (SDAISAs) are statistical entities for state recognized American Indian tribes that do not have a state recognized land base (reservation). SDAISAs are identified and delineated for the U.S. Census Bureau by a state liaison identified by the governor's office in each state. SDAISAs generally encompass a compact and contiguous area that contains a concentration of people who identify with a state recognized American Indian tribe and in which there is structured or organized tribal activity. A SDAISA may not be located in more than one state unless the tribe is recognized by both states, and it may not include area within an American Indian reservation, off-reservation trust land, Alaska Native village statistical area, tribal designated statistical area (TDSA), or Oklahoma tribal statistical area.

The U.S. Census Bureau established SDAISAs as a new geographic statistical entity for Census 2000, to differentiate between state recognized tribes without a land base and federally recognized tribes without a land base. For the 1990 census, all such tribal entities had been identified as TDSAs.

Each SDAISA is assigned a four-digit census code ranging from 9500 through 9999 in alphabetical sequence of SDAISA name nationwide. Each SDAISA also is assigned a five-digit Federal Information Processing Standards (FIPS) code in alphabetical order within state.

Tribal designated statistical areas (TDSAs) are statistical entities identified and delineated for the U.S. Census Bureau by federally recognized American Indian tribes that do not currently have a federally recognized land base (reservation or off-reservation trust land). A TDSA generally encompasses a compact and contiguous area that contains a concentration of people who identify with a federally recognized American Indian tribe and in which there is structured or organized tribal activity. A TDSA may be located in more than one state, and it may not include area within an American Indian reservation, off-reservation trust land, Alaska Native village statistical area, state designated American Indian statistical area (SDAISA), or Oklahoma tribal statistical area.

The U.S. Census Bureau first reported data for TDSAs in conjunction with the 1990 census, when both federally and state recognized tribes could identify and delineate TDSAs. TDSAs now apply only to federally recognized tribes. State recognized tribes without a land base, including those that were TDSAs in 1990, are identified as SDAISAs, a new geographic entity for Census 2000.

Each TDSA is assigned a four-digit census code ranging from 8000 through 8999 in alphabetical sequence of TDSA name nationwide. Each TDSA also is assigned a five-digit Federal Information Processing Standards (FIPS) code in alphabetical order within state; because FIPS codes are assigned within each state, the FIPS code is different in each state for TDSAs that extend into more than one state.

A census block group (BG) is a cluster of census blocks having the same first digit of their four-digit identifying numbers within a census tract. (See also Census Tract.) For example, block group 3 (BG 3) within a census tract includes all blocks numbered from 3000 to 3999. BGs generally contain between 600 and 3,000 people, with an optimum size of 1,500 people. Most BGs were delineated by local participants as part of the U.S. Census Bureau's Participant Statistical Areas Program. The U.S. Census Bureau delineated BGs only where a local, state, or tribal government declined to participate or where the U.S. Census Bureau could not identify a potential local or tribal participant. BGs never cross the boundaries of states, counties, or statistically equivalent entities, except for a BG delineated by American Indian tribal authorities, and then only when tabulated within the American Indian hierarchy. (See also Tribal Block Group.) BGs never cross the boundaries of census tracts, but may cross the boundary of any other geographic entity required as a census block boundary.

In decennial census data tabulations, a BG may be split for statistical purposes for every unique combination of American Indian area, Alaska Native area, Hawaiian home land, congressional district, county subdivision, place, voting district, or other tabulation entity. For example, if BG 3 is partly in a city and partly outside the city, there are separate tabulated records for each portion of BG 3. BGs are used in tabulating data nationwide, as was done for the 1990 census, for all block-numbered areas in the 1980 census, and for selected areas in the 1970 census. For statistical purposes, BGs are a substitute for the enumeration districts (EDs) used for reporting data in many parts of the United States for the 1970 and 1980 censuses and in all areas before 1970.

A tribal block group (BG) is a cluster of census blocks having the same first digit of their four-digit identifying numbers and are within a single tribal census tract. For example, tribal BG 3 consists of all blocks within tribal tract 9406 numbered from 3000 to 3999. Where a federally recognized American Indian reservation and/or off-reservation trust land crosses county and/or state lines, the same tribal BG may be assigned on both sides of the state/county boundary within a tribal census tract that is numbered from 9400 to 9499. The optimum size for a tribal BG is 1,000 people; it must contain a minimum of 300 people. (See also Block Group.)

The difference between a tribal BG and a nontribal BG is in the hierarchical presentation of the data. A tribal BG is part of the American Indian hierarchy; that is, the tribal BG is within a tribal census tract that is within a federally recognized American Indian reservation and/or off-reservation trust land.

Census divisions are groupings of states that are subdivisions of the four census regions. (See also Census Region.) There are nine census divisions, which the U.S. Census Bureau adopted in 1910 for the presentation of data. Each census division is identified by a one-digit census code.

Puerto Rico and the Island Areas are not part of any census region or census division.

Census regions are groupings of states that subdivide the United States for the presentation of data. There are four census regions- Northeast, Midwest, South, and West. Each of the four census regions is divided into two or more census divisions. (See also Census Divisions.) Before 1984, the Midwest region was named the North Central region. From 1910, when census regions were established, through the 1940s, there were three census regions- North, South, and West. Each census region is identified by a single-digit census code. Puerto Rico and the Island Areas are not part of any census region or census division.

Census tracts are small, relatively permanent statistical subdivisions of a county delineated by local participants as part of the U.S. Census Bureau's Participant Statistical Areas Program. The U.S. Census Bureau delineated census tracts in situations where no local participant existed or where local or tribal governments declined to participate. The primary purpose of census tracts is to provide a stable set of geographic units for the presentation of decennial census data. This is the first decennial census for which the entire United States is covered by census tracts. For the 1990 census, some counties had census tracts and others had block numbering areas (BNAs). In preparation for Census 2000, all BNAs were replaced by census tracts, which may or may not cover the same areas.

Census tracts generally have between 1,500 and 8,000 people, with an optimum size of 4,000 people. Counties with fewer people have a single census tract.) When first delineated, census tracts are designed to be homogeneous with respect to population characteristics, economic status, and living conditions. The spatial size of census tracts varies widely depending on the density of settlement. Census tract boundaries are delineated with the intention of being maintained over many decades so that statistical comparisons can be made from decennial census to decennial census. However, physical changes in street patterns caused by highway construction, new developments, and so forth, may require occasional boundary revisions. In addition, census tracts occasionally are split due to population growth or combined as a result of substantial population decline.

Census tracts are identified by a four-digit basic number and may have a two-digit numeric suffix; or example, 6059.02. The decimal point separating the four-digit basic tract number from the two-digit suffix is shown in the printed reports and on census maps. In computer-readable files, the decimal point is implied. Many census tracts do not have a suffix; in such cases, the suffix field is either left blank or is zero-filled. Leading zeros in a census tract number (for example, 002502) are shown only in computer-readable files. Census tract suffixes may range from .01 to .98. For the 1990 census, the .99 suffix was reserved for census tracts/block numbering areas (BNAs) that contained only crews-of-vessels population; for Census 2000, the crews-of-vessels population is part of the related census tract.

Census tract numbers range from 1 to 9999 and are unique within a county or statistically equivalent entity. The U.S. Census Bureau reserves the basic census tract numbers 9400 to 9499 for census tracts delineated within or to encompass American Indian reservations and off-reservation trust lands that exist in multiple states or counties. The number 0000 in computer-readable files identifies a census tract delineated to provide complete coverage of water area in territorial seas and the Great Lakes.

Tribal census tracts are small, relatively permanent statistical subdivisions of a federally recognized American Indian reservation and/or off-reservation trust land. The optimum size for a tribal census tract is 2,500 people; it must contain a minimum of 1,000 people. Where a federally recognized American Indian reservation or off-reservation trust land crosses county or state lines, the same tribal census tract number may be assigned on both sides of the state/county boundary. The U.S. Census Bureau uses the census tract numbers 9400 to 9499 for tribal census tracts that cross state/county boundaries and are within or encompassing American Indian reservations and off-reservation trust land. (See also Census Tract.)

The difference between a tribal census tract and a nontribal census tract is in the hierarchical presentation of the data. A tribal census tract is part of the American Indian hierarchy; that is, the tribal census tract is within a federally recognized American Indian reservation and/or off-reservation trust land.

Congressional districts (CDs) are the 435 areas from which people are elected to the U.S. House of Representatives. After the apportionment of congressional seats among the states, based on census population counts, each state is responsible for establishing CDs for the purpose of electing representatives. Each CD is to be as equal in population to all other CDs in the state as practicable.

The CDs in effect at the time of Census 2000 were those of the 106th Congress, whose session began in January 1999. The boundaries were identical to those reflected in the 107th CD boundary files. The CDs for the 103rd Congress (January 1993 to 1995) were the first to reflect redistricting based on the 1990 census. The 103rd CDs remained in effect through Census 2000, except where a state initiative or a court-ordered redistricting required a change. Six states redistricted for the 104th Congress (Georgia, Louisiana, Maine, Minnesota, South Carolina, and Virginia), five states redistricted for the 105th Congress (Florida, Georgia, Kentucky, Louisiana, and Texas), and three states (New York, North Carolina, and Virginia) redistricted for the 106th Congress. In North Carolina the "1998 Congressional Plan A" was used for the 1998 congressional elections. It was created in response to a court ruling which held the 1997 plan, "97 House/Senate Plan A," unconstitutional. These boundaries are reflected in the 106th CD boundary files. The Supreme Court has since reversed that lower court ruling and the 1997 plan, "97 House/Senate Plan A," (reflected in the 107th CD boundary files) was used for the 2000 North Carolina congressional elections. The 108th Congress is the first to reflect reapportionment and redistricting based on Census 2000 data.
CDs are identified with a two-digit Federal Information Processing Standards (FIPS) code. The code "00" is used for states with a single representative.

American Samoa, Guam, the Virgin Islands (U.S.), and the District of Columbia are represented in the House of Representatives by a delegate, and Puerto Rico by a resident commissioner, all of whom may not vote on the floor of the House of Representatives, but may vote on legislation as it is considered by committees to which they have been named. The two-digit FIPS code "98" is used to identify such representational areas. The Northern Mariana Islands does not have representation in Congress. The FIPS code "99" identifies areas with no representation in Congress.

Places, for the reporting of decennial census data, include census designated places, consolidated cities, and incorporated places.Each place is assigned a five-digit Federal Information Processing Standards (FIPS) code in alphabetical order within each state.

Census designated places (CDPs) are delineated for each decennial census as the statistical counterparts of incorporated places. CDPs are delineated to provide data for settled concentrations of population that are identifiable by name but are not legally incorporated under the laws of the state in which they are located. The boundaries usually are defined in cooperation with local or tribal officials. These boundaries, which usually coincide with visible features or the boundary of an adjacent incorporated place or other legal entity boundary, have no legal status, nor do these places have officials elected to serve traditional municipal functions. CDP boundaries may change from one decennial census to the next with changes in the settlement pattern; a CDP with the same name as in an earlier census does not necessarily have the same boundary.
There are no population size requirements for the CDPs designated in conjunction with Census 2000. For the 1990 census and earlier censuses, the U.S. Census Bureau required CDPs to qualify on the basis of various minimum population size criteria.

Beginning with the 1950 census, the U.S. Census Bureau, in cooperation with state and local governments (and American Indian tribal officials starting with the 1990 census), identified and delineated boundaries and names for CDPs. In the data products issued in conjunction with Census 2000, the name of each such place is followed by "CDP," as was the case for the 1990 and 1980 censuses. In the data products issued in conjunction with the 1950, 1960, and 1970 censuses, these places were identified by "(U)," meaning "unincorporated place."

Hawaii is the only state that has no incorporated places recognized by the U.S. Census Bureau. All places shown in the data products for Hawaii are CDPs. By agreement with the state of Hawaii, the U.S. Census Bureau does not show data separately for the city of Honolulu, which is coextensive with Honolulu County.

There are no incorporated places in Puerto Rico; instead, the U.S. Census Bureau provides decennial census data for two types of census designated places (CDPs): (1) zonas urbanas, representing the governmental center of each municipio and (2) comunidades, representing other settlements. For Census 2000, there are no minimum population size requirements for CDPs. (For the 1990 census, the U.S. Census Bureau had required comunidades to have at least 1,000 people.)

Each CDP is assigned a five-digit Federal Information Processing Standards (FIPS) code, based on the alphabetical order of the CDP name within each state. If CDP names are duplicated within a state and they represent distinctly different areas, a separate code is assigned to each CDP name alphabetically by primary county in which each place is located.

A consolidated government is a unit of local government for which the functions of an incorporated place and its county or minor civil division (MCD) have merged. The legal aspects of this action may result in both the primary incorporated place and the county or MCD continuing to exist as legal entities, even though the county or MCD performs few or no governmental functions and has few or no elected officials. Where this occurs, and where one or more other incorporated places in the county or MCD continue to function as separate governments, even though they have been included in the consolidated government, the primary incorporated place is referred to as a "consolidated city."

The presentation of data for consolidated cities varies depending on the geographic presentation. In some hierarchical presentations, consolidated cities are not shown. These presentations include the incorporated places within the consolidated city and the "consolidated city (balance)." Although hierarchical presentations do not show the consolidated city, the data for it are the same as the county or county subdivision with which it is coextensive. Other hierarchical presentations do not show the consolidated city, county or county subdivision, and (balance) as separate entities.

For inventory geographic presentations, the consolidated city appears at the end of the listing of places. The data for the consolidated city include the data for all places that are part of and within the consolidated city. The "consolidated city (balance)" entry shows the data for the portion of the consolidated government minus the incorporated places, and is shown in alphabetical sequence with other places that comprise the consolidated city. For statistical purposes, these entities are treated as statistically equivalent to a place and have no legal basis or functions.

In summary presentations by size of place, the consolidated city is not included. The places within consolidated cities are categorized by their size, as is the "consolidated city (balance)." A few incorporated places are partially inside and partially outside a consolidated city. Data tabulations by incorporated place will include all territory within the incorporated place, while the tabulation for the incorporated place within a consolidated city is only for part of the incorporated place.

Each consolidated city is assigned a five-digit Federal Information Processing Standards (FIPS) code that is unique within state. The incorporated places and the "consolidated city (balance)" also are assigned five-digit FIPS place codes that are unique within state. The code assigned to each incorporated place within a consolidated city is the same as its regular incorporated place code; an incorporated place that is partially included in a consolidated city does not have a different code for the portions inside and outside the consolidated city. FIPS codes are assigned based on alphabetical sequence within each state.

Incorporated places recognized in decennial census data products are those reported to the U.S. Census Bureau as legally in existence on January 1, 2000, under the laws of their respective states, as cities, boroughs, towns, and villages, with the following exceptions: the towns in the New England states, New York, and Wisconsin, and the boroughs in New York are recognized as minor civil divisions for statistical purposes; the boroughs in Alaska are county equivalents for decennial census statistical presentation purposes. In four states (Maryland, Missouri, Nevada, and Virginia), there are one or more incorporated places known as "independent cities" that are primary divisions of a state and legally not part of any county. For statistical purposes, the U.S. Census Bureau may treat an independent city as a county equivalent, county subdivision, and place.

The U.S. Census Bureau treats the villages in American Samoa as incorporated places because they have their own officials, who have specific legal powers as authorized in the American Samoa Code. The village boundaries are traditional rather than being specific, legally defined locations. There are no incorporated places in Guam and the Northern Mariana Islands. The Census Bureau treats the three towns in the Virgin Islands of the United States as incorporated places.

There are a few incorporated places that do not have a legal description. An incorporated place is established to provide governmental functions for a concentration of people as opposed to a minor civil division, which generally is created to provide services or administer an area without regard, necessarily, to population.
Each incorporated place is assigned a five-digit Federal Information Processing Standards (FIPS) code, based on the alphabetical order of the incorporated place name within each state. If incorporated place names are duplicated within a state and they represent distinctly different areas, a separate code is assigned to each incorporated place name alphabetically by primary county in which each incorporated place is located, or if both incorporated places are in the same county, alphabetically by their legal description (for example, "city" before "village").

The primary legal divisions of most states are termed "counties." In Louisiana, these divisions are known as "parishes." In Alaska, which has no counties, the statistically equivalent entities are census areas, city and boroughs (Juneau City and Borough) a municipality (Anchorage), and organized boroughs. Census are delineated cooperatively for statistical purposes by the state of Alaska and the U.S. Census Bureau. In four states (Maryland, Missouri, Nevada, and Virginia), there are one or more incorporated places that are independent of any county organization and thus constitute primary divisions of their states; these incorporated places are known as "independent cities" and are treated as equivalent to counties for statistical purposes. (For some statistical purposes they may be treated as county subdivisions and places.) The District of Columbia has no primary divisions, and the entire area is considered equivalent to a county for statistical purposes. The primary legal divisions of Puerto Rico are termed "municipios" and are treated by the U.S. Census Bureau, for statistical purposes, as the equivalent of a county in the United States.

Each county and statistically equivalent entity is assigned a three-digit Federal Information Processing Standards (FIPS) code that is unique within state or state equivalent. These codes are assigned in alphabetical order of county or county equivalent within state, except for the independent cities, which are assigned codes higher than and following the listing of counties.

County subdivisions are the primary divisions of counties and statistically equivalent entities for the reporting of decennial census data. They include census county divisions, census subareas, minor civil divisions (including barrios and barrio-pueblos in Puerto Rico), and unorganized territories. Each county subdivision is assigned a five-digit Federal Information Processing Standards (FIPS) code in alphabetical order within each state.

Census county divisions (CCDs) are county subdivisions that were delineated by the U.S. Census Bureau, in cooperation with state and local officials for purposes of presenting statistical data. CCDs have been established in 21 states where there are no legally established minor civil divisions (MCDs), where the MCDs do not have governmental or administrative purposes, where the boundaries of the MCDs change frequently, and/or where the MCDs generally are not known to the public. CCDs have no legal functions and are not governmental units.

The boundaries of CCDs usually are delineated to follow visible features, and coincide with census tracts where applicable. (In rare instances, two CCDs may constitute a single census tract.) The name of each CCD is based on a place, county, or well-known local name that identifies its location. CCDs have been established in the following 21 states: Alabama, Arizona, California, Colorado, Delaware, Florida, Georgia, Hawaii, Idaho, Kentucky, Montana, Nevada, New Mexico, Oklahoma, Oregon, South Carolina, Tennessee, Texas, Utah, Washington, and Wyoming.

Census subareas are statistical subdivisions of boroughs, census areas, city and boroughs, and the municipality (entities that are statistically equivalent to counties) in Alaska. Census subareas are delineated cooperatively by the state of Alaska and the U.S. Census Bureau. They were first used for data presentation purposes as part of the 1980 census.

Minor civil divisions (MCDs) are the primary governmental or administrative divisions of a county or county equivalent in many states. MCDs represent many different kinds of legal entities with a wide variety of governmental and/or administrative functions. MCDs are variously designated as American Indian reservations, assessment districts, boroughs, charter townships, election districts, election precincts, gores, grants, locations, magisterial districts, parish governing authority districts, plantations, precincts, purchases, road districts, supervisor's districts, towns, and townships. In some states, all or some incorporated places are not located in any MCD (independent places) and thus serve as MCDs in their own right. In other states, incorporated places are part of the MCDs in which they are located (dependent places), or the pattern is mixed- some incorporated places are independent of MCDs and others are included within one or more MCDs. Independent cities, which are statistically equivalent to a county, also are treated as a separate MCD equivalent in states containing MCDs. In Maine and New York, there are American Indian reservations and off-reservation trust lands that serve as MCD equivalents; a separate MCD is created in each case where the American Indian area crosses a county boundary.

The U.S. Census Bureau recognizes MCDs in the following 28 states: Arkansas, Connecticut, Illinois, Indiana, Iowa, Kansas, Louisiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Nebraska, New Hampshire, New Jersey, New York, North Carolina, North Dakota, Ohio, Pennsylvania, Rhode Island, South Dakota, Vermont, Virginia, West Virginia, and Wisconsin. The District of Columbia has no primary divisions, and the city of Washington is considered equivalent to an MCD for statistical purposes. Arlington County, VA, also has no MCDs and the entire county is designated as an MCD with the name Arlington. The MCDs in 12 states (Connecticut, Maine, Massachusetts, Michigan, Minnesota, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, and Wisconsin) also serve as general-purpose local governments that generally can perform the same governmental functions as incorporated places. The U.S. Census Bureau presents data for these MCDs in all data products in which it provides data for places.

Unorganized territories occur in 10 minor civil division (MCD) states (Arkansas, Indiana, Iowa, Louisiana, Maine, Minnesota, North Carolina, North Dakota, Ohio, and South Dakota) where portions of counties are not included in any legally established MCD or independent incorporated place. The U.S. Census Bureau recognizes such separate pieces of territory as one or more separate county subdivisions for statistical purposes. It assigns each unorganized territory a descriptive name, followed by the designation "unorganized territory." Unorganized territories were first used for statistical purposes in conjunction with the 1960 census.

In Puerto Rico, the U.S. Census Bureau recognizes barrios and barrio-pueblos as the primary legal divisions of municipios (census county equivalents). One barrio in each municipio (except Florida, Ponce, and San Juan) is identified as the barrio-pueblo, the area that represented the seat of the government at the time Puerto Rico formalized the municipio and barrio boundaries in the late 1940's. These entities are similar to the minor civil divisions (MCDs) used for reporting decennial census data in 28 states of the United States.

Subbarrios in 23 municipios (census county equivalents) in Puerto Rico are the primary legal subdivisions of the barrios-pueblo and some barrios (census MCD equivalents). The U.S. Census Bureau presents the same types of Census 2000 data for these "sub-MCDs" as it does for the barrios and barrios-pueblo. (There is no geographic entity in the United States equivalent to the subbarrio.)

Each barrio, barrio-pueblo, and subbarrio is assigned a five-digit Federal Information Processing Standards (FIPS) code in alphabetical order within Puerto Rico.

Places, for the reporting of decennial census data, include census designated places, consolidated cities, and incorporated places.Each place is assigned a five-digit Federal Information Processing Standards (FIPS) code in alphabetical order within each state.

Census designated places (CDPs) are delineated for each decennial census as the statistical counterparts of incorporated places. CDPs are delineated to provide data for settled concentrations of population that are identifiable by name but are not legally incorporated under the laws of the state in which they are located. The boundaries usually are defined in cooperation with local or tribal officials. These boundaries, which usually coincide with visible features or the boundary of an adjacent incorporated place or other legal entity boundary, have no legal status, nor do these places have officials elected to serve traditional municipal functions. CDP boundaries may change from one decennial census to the next with changes in the settlement pattern; a CDP with the same name as in an earlier census does not necessarily have the same boundary. There are no population size requirements for the CDPs designated in conjunction with Census 2000. For the 1990 census and earlier censuses, the U.S. Census Bureau required CDPs to qualify on the basis of various minimum population size criteria.Beginning with the 1950 census, the U.S. Census Bureau, in cooperation with state and local governments (and American Indian tribal officials starting with the 1990 census), identified and delineated boundaries and names for CDPs. In the data products issued in conjunction with Census 2000, the name of each such place is followed by "CDP," as was the case for the 1990 and 1980 censuses. In the data products issued in conjunction with the 1950, 1960, and 1970 censuses, these places were identified by "(U)," meaning "unincorporated place."

Hawaii is the only state that has no incorporated places recognized by the U.S. Census Bureau. All places shown in the data products for Hawaii are CDPs. By agreement with the state of Hawaii, the U.S. Census Bureau does not show data separately for the city of Honolulu, which is coextensive with Honolulu County.

There are no incorporated places in Puerto Rico; instead, the U.S. Census Bureau provides decennial census data for two types of census designated places (CDPs): (1) zonas urbanas, representing the governmental center of each municipio and (2) comunidades, representing other settlements. For Census 2000, there are no minimum population size requirements for CDPs. (For the 1990 census, the U.S. Census Bureau had required comunidades to have at least 1,000 people.)

Each CDP is assigned a five-digit Federal Information Processing Standards (FIPS) code, based on the alphabetical order of the CDP name within each state. If CDP names are duplicated within a state and they represent distinctly different areas, a separate code is assigned to each CDP name alphabetically by primary county in which each place is located.

A consolidated government is a unit of local government for which the functions of an incorporated place and its county or minor civil division (MCD) have merged. The legal aspects of this action may result in both the primary incorporated place and the county or MCD continuing to exist as legal entities, even though the county or MCD performs few or no governmental functions and has few or no elected officials. Where this occurs, and where one or more other incorporated places in the county or MCD continue to function as separate governments, even though they have been included in the consolidated government, the primary incorporated place is referred to as a "consolidated city."

The presentation of data for consolidated cities varies depending on the geographic presentation. In some hierarchical presentations, consolidated cities are not shown. These presentations include the incorporated places within the consolidated city and the "consolidated city (balance)." Although hierarchical presentations do not show the consolidated city, the data for it are the same as the county or county subdivision with which it is coextensive. Other hierarchical presentations do not show the consolidated city, county or county subdivision, and (balance) as separate entities.

For inventory geographic presentations, the consolidated city appears at the end of the listing of places. The data for the consolidated city include the data for all places that are part of and within the consolidated city. The "consolidated city (balance)" entry shows the data for the portion of the consolidated government minus the incorporated places, and is shown in alphabetical sequence with other places that comprise the consolidated city. For statistical purposes, these entities are treated as statistically equivalent to a place and have no legal basis or functions.

In summary presentations by size of place, the consolidated city is not included. The places within consolidated cities are categorized by their size, as is the "consolidated city (balance)." A few incorporated places are partially inside and partially outside a consolidated city. Data tabulations by incorporated place will include all territory within the incorporated place, while the tabulation for the incorporated place within a consolidated city is only for part of the incorporated place.
Each consolidated city is assigned a five-digit Federal Information Processing Standards (FIPS) code that is unique within state. The incorporated places and the "consolidated city (balance)" also are assigned five-digit FIPS place codes that are unique within state. The code assigned to each incorporated place within a consolidated city is the same as its regular incorporated place code; an incorporated place that is partially included in a consolidated city does not have a different code for the portions inside and outside the consolidated city. FIPS codes are assigned based on alphabetical sequence within each state.

Incorporated places recognized in decennial census data products are those reported to the U.S. Census Bureau as legally in existence on January 1, 2000, under the laws of their respective states, as cities, boroughs, towns, and villages, with the following exceptions: the towns in the New England states, New York, and Wisconsin, and the boroughs in New York are recognized as minor civil divisions for statistical purposes; the boroughs in Alaska are county equivalents for decennial census statistical presentation purposes. In four states (Maryland, Missouri, Nevada, and Virginia), there are one or more incorporated places known as "independent cities" that are primary divisions of a state and legally not part of any county. For statistical purposes, the U.S. Census Bureau may treat an independent city as a county equivalent, county subdivision, and place.

The U.S. Census Bureau treats the villages in American Samoa as incorporated places because they have their own officials, who have specific legal powers as authorized in the American Samoa Code. The village boundaries are traditional rather than being specific, legally defined locations. There are no incorporated places in Guam and the Northern Mariana Islands. The Census Bureau treats the three towns in the Virgin Islands of the United States as incorporated places.

There are a few incorporated places that do not have a legal description. An incorporated place is established to provide governmental functions for a concentration of people as opposed to a minor civil division, which generally is created to provide services or administer an area without regard, necessarily, to population.
Each incorporated place is assigned a five-digit Federal Information Processing Standards (FIPS) code, based on the alphabetical order of the incorporated place name within each state. If incorporated place names are duplicated within a state and they represent distinctly different areas, a separate code is assigned to each incorporated place name alphabetically by primary county in which each incorporated place is located, or if both incorporated places are in the same county, alphabetically by their legal description (for example, "city" before "village").

Metropolitan and micropolitan statistical areas (referred to generically as "core based statistical areas" or CBSAs) are statistical geographic areas defined by the federal Office of Management and Budget (OMB), following a set of official standards published in the Federal Register. http://www.census.gov/population/www/estimates/00-32997.pdfTo meet the needs of various users for standard units at various geographic scales, OMB's standards provide for a flexible framework of area definitions that includes, in addition to metropolitan and micropolitan statistical areas, metropolitan divisions, combined statistical areas, New England city and town areas (NECTAs), NECTA divisions, and combined NECTAs. Documentation of the metropolitan and micropolitan statistical area standards and how they are applied is available on the Census Bureau's websitehttp://www.census.gov/population/www/estimates/metroarea.html or from the Population Distribution Branch, Population Division, U.S. Census Bureau, Washington, DC 20233-8800, telephone (301) 763-2419.Each metropolitan or micropolitan statistical area consists of a core area containing a substantial population nucleus, together with adjacent communities having a high degree of economic and social integration with that core. Metropolitan statistical areas contain at least one U.S. Census Bureau-defined urbanized area of 50,000 or more population; micropolitan statistical areas contain at least one Census Bureau-defined urban cluster of at least 10,000 and less than 50,000 population. If specified criteria are met, a metropolitan statistical area containing a single urbanized area with a population of 2.5 million or more may be subdivided into metropolitan divisions, which function as distinct social and economic areas within the larger metropolitan statistical area. The territory, population, and housing units in metropolitan statistical areas are referred to as "metropolitan." The metropolitan category is subdivided into "inside principal city" and "outside principal city." The territory, population, and housing units located outside territory designated "metropolitan" are referred to as "nonmetropolitan;" the latter designation also include micropolitan statistical areas. These categories do not equate to an urban/rural classification; indeed, all metropolitan and micropolitan statistical areas and territory located outside CBSAs contain a mixture of urban and rural territory, population, and housing units. While it is the case that the populations of metropolitan statistical areas tend to be predominantly urban, according to Census 2000 data, over 50 percent of the U.S. rural population resides within metropolitan statistical areas.

Combined statistical areas are groupings of adjacent metropolitan and/or micropolitan statistical areas that have social and economic ties as measured by commuting to work, but at lower levels than are found among counties within individual metropolitan and micropolitan statistical areas. Combined statistical areas can be characterized as representing larger regions that reflect broader social and economic interactions, such as wholesaling, commodity distribution, and weekend recreation activities, and are likely to be of considerable interest to regional authorities and the private sector.

In view of the importance of cities and towns in New England, OMB's standards also provide for a set of geographic areas that are defined using cities and towns in the six New England states. New England city and town areas (NECTAs), NECTA divisions, and combined NECTAs provide a city- and town-based set of areas conceptually similar to the county-based metropolitan and micropolitan statistical areas, metropolitan divisions, and combined statistical areas.

OMB's standards provide for the identification of one or more principal cities within each metropolitan statistical area, micropolitan statistical area, and NECTA. (The term "principal city" replaces "central city," the term used in previous standards.) Principal cities encompass both incorporated places and census designated places (CDPs). In each metropolitan statistical area, micropolitan statistical area, and NECTA the largest place and, in some cases, additional places are designated as "principal cities" under the official standards. A principal city does not include any part of that place that extends outside the metropolitan statistical area, micropolitan statistical area, or NECTA boundary.

The title of a metropolitan statistical area, micropolitan statistical area, or NECTA contains the name of its largest principal city and the names of up to two additional principal cities. The title of a metropolitan division or NECTA division may contain the names of up to three principal cities, as determined above, or the names of up to three counties (or cities and towns in the case of a NECTA division), sequenced in order of descending population size. The title of each combined statistical area or combined NECTA contains the names of the largest principal cities in the combination, provided the title does not duplicate the title of a metropolitan or micropolitan statistical area or NECTA. Regional names are permitted, and local opinion is considered, when identifying the title of a combined statistical area or combined NECTA. The titles for all metropolitan and micropolitan statistical areas also contain the U.S. Postal Service's abbreviation for the name of each state in which the area is located.

Each metropolitan and micropolitan statistical area, metropolitan division, NECTA, and NECTA division is assigned a five-digit code, in alphabetical order nationwide. Metropolitan divisions and NECTA divisions are distinguished by a code ending in "4." Codes for metropolitan and micropolitan statistical areas and metropolitan divisions fall within the 10000 to 59999 range. NECTA and NECTA division codes fall within the 70000 to 79999 range. Each combined statistical area and combined NECTA is assigned a three-digit code, in alphabetical order nationwide. Codes for combined statistical areas fall within the 100 to 599 range. Codes for combined NECTAs fall within the 700 to 799 range.

The general concept of a metropolitan area (MA) is one of a large population nucleus, together with adjacent communities that have a high degree of economic and social integration with that nucleus. Some MAs are defined around two or more nuclei.
The MAs and the central cities within an MA are designated and defined by the federal Office of Management and Budget (OMB), following a set of official standards that are published in a Federal Register Notice. These standards were developed by the interagency Federal Executive Committee on Metropolitan Areas, with the aim of producing definitions that are as consistent as possible for all MAs nationwide.
Each MA must contain either a place with a minimum population of 50,000 or a U.S. Census Bureau-defined urbanized area and a total MA population of at least 100,000 (75,000 in New England). An MA contains one or more central counties. An MA also may include one or more outlying counties that have close economic and social relationships with the central county. An outlying county must have a specified level of commuting to the central counties and also must meet certain standards regarding metropolitan character, such as population density, urban population, and population growth. In New England, MAs consist of groupings of cities and towns rather than whole counties.

The territory, population, and housing units in MAs are referred to as "metropolitan." The metropolitan category is subdivided into "inside central city" and "outside central city." The territory, population, and housing units located outside territory designated "metropolitan" are referred to as "nonmetropolitan." The metropolitan and nonmetropolitan classification cuts across the other hierarchies; for example, generally there are both urban and rural territory within both metropolitan and nonmetropolitan areas.

To meet the needs of various users, the standards provide for a flexible structure of metropolitan definitions that classify each MA either as a metropolitan statistical area (MSA) or as a consolidated metropolitan statistical area (CMSA) divided into primary metropolitan statistical areas (PMSAs). In New England, there also is an alternative county-based definition of MSAs known as the New England County Metropolitan Areas (NECMAs). Documentation of the MA standards and how they are applied is available from the Population Distribution Branch, Population Division, U.S. Census Bureau, Washington, DC 20233-8800, telephone (301) 457-2419.

Metropolitan statistical areas (MSAs) are metropolitan areas (MAs) that are not closely associated with other MAs. These areas typically are surrounded by nonmetropolitan counties (county subdivisions in New England).

If an area that qualifies as a metropolitan area (MA) has more than one million people, two or more primary metropolitan statistical areas (PMSAs) may be defined within it. Each PMSA consists of a large urbanized county or cluster of counties (cities and towns in New England) that demonstrate very strong internal economic and social links, in addition to close ties to other portions of the larger area. When PMSAs are established, the larger MA of which they are component parts is designated a consolidated metropolitan statistical area (CMSA). CMSAs and PMSAs are established only where local governments favor such designations for a large MA.

In each metropolitan statistical area and consolidated metropolitan statistical area, the largest place and, in some cases, additional places are designated as "central cities" under the official standards. A few primary metropolitan statistical areas do not have central cities. The largest central city and, in some cases, up to two additional central cities, are included in the title of the metropolitan area (MA); there also are central cities that are not included in an MA title. An MA central city does not include any part of that place that extends outside the MA boundary.

The title of a metropolitan statistical area (MSA) contains the name of its largest central city and up to two additional place names, provided that the additional places meet specified levels of population, employment, and commuting. Generally, a place with a population of 250,000 or more is in the title, regardless of other criteria.
The title of a primary metropolitan statistical area (PMSA) may contain up to three place names, as determined above, or up to three county names, sequenced in order of population size, from largest to smallest. A consolidated metropolitan statistical area (CMSA) title also may include up to three names, the first of which generally is the most populous central city in the area. The second name may be the first city or county name in the most populous remaining PMSA; the third name may be the first city or county name in the next most populous PMSA. A regional designation may be substituted for the second and/or third names in a CMSA title if local opinion supports such a designation and the federal Office of Management and Budget (OMB) deems it to be unambiguous and suitable.

The titles for all metropolitan areas (MAs) also contain the U.S. Postal Service's abbreviation for the name of each state in which the MA is located. Each MA is assigned a four-digit Federal Information Processing Standards (FIPS) code, in alphabetical order nationwide. If the fourth digit of the code is "2," it identifies a CMSA. Additionally, there is a separate set of two-digit FIPS codes for CMSAs, also assigned alphabetically.

New England county metropolitan areas (NECMAs) are defined as a county-based alternative to the city- and town-based New England metropolitan statistical areas (MSAs) and consolidated metropolitan statistical areas (CMSAs). The NECMA defined for an MSA or a CMSA includes:

The county containing the first-named city in that MSA/CMSA title (this county may include the first-named cities of other MSAs/CMSAs as well), and each additional county having at least half its population in the MSAs/CMSAs whose first-named cities are in the previously identified county. NECMAs are not identified for individual primary metropolitan statistical areas (PMSAs).Central cities of a NECMA are those places in the NECMA that qualify as central cities of an MSA or a CMSA. NECMA titles derive from the names of these central cities. Each NECMA is assigned a four-digit Federal Information Processing Standards (FIPS) code.

An urban growth area (UGA) is a legally defined entity in Oregon that the U.S. Census Bureau includes in the TIGER database in agreement with the state. UGAs, which are defined around incorporated places, are used to regulate urban growth. UGA boundaries, which need not follow visible features, are delineated cooperatively by state and local officials and then confirmed in state law. UGAs, which are a pilot project, are a new geographic entity for Census 2000. Each UGA is identified by a five-digit numeric census code, assigned alphabetically by name within Oregon.

A public use microdata area (PUMA) is an area with a decennial census population of 100,000 or more people for which the U.S. Census Bureau provides specially selected extracts of raw data from a small sample of long-form census records screened to protect confidentiality. These extracts are referred to as "public use microdata sample (PUMS)" files. Data users can use these files to create their own statistical tabulations and data summaries. For Census 2000, there are state-level and national PUMS files. The U.S. Census Bureau first provided PUMS information in conjunction with the 1960 census data tabulations.

For Census 2000, state, District of Columbia, Puerto Rico, and Island Area participants, following U.S. Census Bureau criteria, delineated two types of PUMAs within their states. PUMAs of one type comprise areas that contain at least 100,000 people. The PUMS files for these PUMAs contain a 5-percent sample of the long-form records. The other type of PUMAs, super-PUMAs, comprise areas of at least 400,000 people. The sample size is 1 percent for the PUMS files for super-PUMAs.

PUMAs cannot be in more than one state or statistically equivalent entity. The larger 1-percent PUMAs are aggregations of the smaller 5-percent PUMAs. PUMAs of both types, wherever the population size criteria permit, comprise areas that are entirely within or outside metropolitan areas or the central cities of metropolitan areas.

School districts are geographic entities within which state, county, or local officials provide public educational services for the area's residents. The U.S. Census Bureau obtains the boundaries and names for school districts from state officials. The U.S. Census Bureau first provided data for school districts in the 1970 census. For Census 2000, the U.S. Census Bureau tabulated data for three types of school districts: elementary, secondary, and unified. Each school district is assigned a five-digit code that is unique within state. School district codes are assigned by the Department of Education and are not necessarily in alphabetical order by school district name.

States are the primary governmental divisions of the United States. The District of Columbia is treated as a statistical equivalent of a state for decennial census purposes, as are Puerto Rico and the Island Areas: American Samoa, Guam, the Commonwealth if the Northern Mariana Islands, and the Virgin Islands of the United States.Each state and statistically equivalent entity is assigned a two-digit numeric Federal Information Processing Standards (FIPS) code in alphabetical order by state name, followed in alphabetical order by the Island Areas and Puerto Rico.

Each state and statistically equivalent entity also is assigned a two-letter FIPS/U.S. Postal Service code and a two-digit census code. The census code is assigned on the basis of the geographic sequence of each state within each census division; the first digit of the code identifies the respective division, except for Puerto Rico and the Island Areas, which are not assigned to any region or division.

State legislative districts (SLDs) are the areas from which members are elected to state legislatures. The SLDs embody the upper (senate) and lower (house) chambers of the state legislature. (Nebraska has a unicameral legislature and the District of Columbia has a city council, both of which the U.S. Census Bureau treats as upper-chamber legislative areas for the purpose of data presentation. Therefore, there is no data by lower chamber for either Nebraska or the District of Columbia.) A unique census code of up to three characters, identified by state participants, is assigned to each SLD within state. The code "ZZZ" identifies parts of a county in which no SLDs were identified. SLDs are provided to the Census Bureau as part of the Redistricting Data Program. Participation by the states is optional; not all states provided their SLDs for 2000.

A traffic analysis zone (TAZ) is a special area delineated by state and/or local transportation officials for tabulating traffic-related data- especially journey-to-work and place-of-work statistics. A TAZ usually consists of one or more census blocks, block groups, or census tracts. For the 1990 census, TAZs were defined as part of the Census Transportation Planning Package (CTPP). The U.S. Census Bureau first provided data for TAZs in conjunction with the 1980 census, when it identified them as "traffic zones." Each TAZ is identified by a six-character alphanumeric code that is unique within county or statistically equivalent entity. For the 1990 census, TAZ codes were unique within CTPP area, which generally conformed to a metropolitan area.

An urbanized area (UA) consists of densely settled territory that contains 50,000 or more people. A UA may contain both place and nonplace territory. The U.S. Census Bureau delineates UAs to provide a better separation of urban and rural territory, population, and housing in the vicinity of large places. At least 35,000 people in a UA must live in an area that is not part of a military reservation.

For Census 2000, UA delineations constitute a "zero-based" approach that requires no "grandfathering" of UA boundaries from the 1990 census. Because of the more stringent density requirements (and the less restrictive extended place criteria), some territory that was classified as urbanized for the 1990 census has been reclassified as rural. In addition, some areas that were identified as UAs for the 1990 census have been reclassified as urban clusters.

The title of a UA may contain up to three incorporated place names, and will include the two-letter U.S. Postal Service abbreviation for each state into which the UA extends. However, if the UA does not contain an incorporated place, the UA title will include the single name of the geographic entity that occurs first from the following list: census designated place, minor civil division, or populated place recognized by the U.S. Geological Survey.

Each UA is assigned a five-digit census code in alphabetical sequence on a nationwide basis, interspersed with the codes for urban clusters (UCs), also in alphabetical sequence. For the 1990 census, the U.S. Census Bureau assigned a four-digit UA code based on the MA codes. For Census 2000, a separate flag is included in data tabulation files to differentiate between UAs and UCs. In printed reports, this differentiation is included in the name.

Voting district (VTD) is the generic name for geographic entities, such as precincts, wards, and election districts, established by state, local, and tribal governments for the purpose of conducting elections. States participating in the Census 2000 Redistricting Data Program as part of Public Law 94-171 (1975) may provide boundaries, codes, and names for their VTDs to the U.S. Census Bureau. The U.S. Census Bureau first reported data for VTDs following the 1980 census. Because the U.S. Census Bureau requires that VTDs follow boundaries of census blocks, participating states often adjusted the boundaries of the VTDs they submit for data tabulation purposes to conform to census block boundaries. If requested by the participating state, the U.S. Census Bureau identifies these "adjusted" VTDs as "pseudo-VTDs." For Census 2000, each VTD is identified by a one- to six-character alphanumeric census code that is unique within county. The code "ZZZZZZ" identifies parts of a county in which no VTDs were identified.

A ZIP Code tabulation area (ZCTA) is a statistical geographic entity that approximates the delivery area for a U.S. Postal Service five-digit or three-digit ZIP Code. ZCTAs are aggregations of census blocks that have the same predominant ZIP Code associated with the addresses in the U.S. Census Bureau's Master Address File (MAF). Three-digit ZCTA codes are applied to large contiguous areas for which the U.S. Census Bureau does not have five-digit ZIP Code information in its MAF. ZCTAs do not precisely depict ZIP Code delivery areas, and do not include all ZIP Codes used for mail delivery. The U.S. Census Bureau has established ZCTAs as a new geographic entity similar to, but replacing, data tabulations for ZIP Codes undertaken in conjunction with the 1990 and earlier censuses.

The American Community Survey Summary Files include all detailed tables for all geographic areas published by the 2009 1-Year ACS. The main directory of the American Community Survey' s Summary File product release, located within the file transfer protocol (FTP) site, contains documentation about the Summary Files, information pertaining to the United States, each of the individual states, the District of Columbia, and Puerto Rico. The following list outlines the hierarchical geographic levels contained within the Summary File release.

Please send any technical questions or comments you have via email to: nicholas.m.spanos@census.gov. If you have questions or comments about the American Community Survey, please contact us online at ask.census.gov